Conventional acrylic resin film has employed polymethyl methacrylate (PMMA) suitably in view of excellent transparency, dimensional stability, low hygroscopicity and so on.
However PMMA resin film has a problem that it is poor in heat resistance and deforms when used for long term. This problem is significant as the physical property of the film as itself and also as the polarizing plate, and the liquid crystal display device employing the film. Namely, there are problems that view angle changes or hue change generates because the polarizing plate curls and therefore panel bents as a whole due to the deformation of the film or preferably designed retardation changes when used at a position between the polarizing plate and liquid crystal cells, during the use for long term of the polarizing plate
On the other side, while the acrylic resin film is excellent in transparency and suitable for the optical film, it is not suitable for the retardation film since it has characteristics not to exhibit sufficient retardation in addition to its brittleness. Further there is a problem that certain retardation control agent is not miscible with an acrylic resin solely or cellulose ester resin solely when the retardation is adjusted by adding retardation control agents.
A method to introduce a alicyclic alkyl or a method to obtain a cyclic composition by infra-molecule cycle forming reaction is proposed to dissolve the various problems described above, for example, Patent Documents 1 to 3.
However there are problem in these method that brittleness of the film degraded significantly though heat resistance is improved and productivity is poor since it takes time in synthesize raw materials or there is restrain in film production method.
There is a method to add polycarbonate in view of heat resistance and mechanical strength, however this method is difficult to use for the optical film since solvent to be used is restrained and resins are hard to dissolve each other and easy to form white turbid. See, for example, Patent Document 4.
Patent Document 5 discloses a film having moisture resistance with low cost obtained by blending an acrylic resin with butyl modified acetyl cellulose, however, this film does not overcome sufficiently brittleness of the acrylic resin. Further, the demands for transparency, high heat resistance, brittleness and so on become moreover markedly, according to request for wider display, thinner parts, lower weight, etc.    Patent Document 1: JP-A 2002-012728    Patent Document 2: JP-A 2005-146084    Patent Document 3: JP-A 2007-191706    Patent Document 4: JP-A H05-306344    Patent Document 5: JP-A H05-119217